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It's a 24-105, not 28, so you get a few more mm of width. However, 24 still isn't very wide on a crop sensor camera. Have you also looked at the Canon 17-55mm f/2.8 IS? I'm not sure how it compares to the Tamron. I like the range, though, for a walkabout lens on a crop camera. I have the Canon for my 50D. As far as I'm concerned it's an "L" lens of the EF-S variety. Very sharp and solidly built. It's $1050 on Amazon right now, but you can pick one up in the Buy & Sell forum on here for around $700.
For years I used the Canon 28-135mm lens as my walkabout. It had OK reach for things other than birds, but it was missing a lot of width. I'm happier now with 17mm on the wide end.